There are several ways to use an op-amp. The op-amp closest to the RCAs is being used as a buffer. The input and output are identical. The second op-amp is acting as an inverter. The output is fed into the inverting input instead of the non-inverting input (as it is on the first op-amp).
Op-amps are designed to make the inverting input match the non-inverting input. When using the inverting input for the signal and the non-inverting input as a reference (no signal, typically connected to ground), there will be no visible signal on either input.
Do you still have weak audio on one channel?
If so, touch the black probe to the small black wire and the red probe to each of the 4 speaker wires. Which one has significantly lower voltage than the other 3?
Op-amps are designed to make the inverting input match the non-inverting input. When using the inverting input for the signal and the non-inverting input as a reference (no signal, typically connected to ground), there will be no visible signal on either input.
Do you still have weak audio on one channel?
If so, touch the black probe to the small black wire and the red probe to each of the 4 speaker wires. Which one has significantly lower voltage than the other 3?
Confirm that the voltage on pins 1 and 7 are all equal (I think that's what you found with the Fluke).
If so, post the AC voltage on all but pins 4 and 8 on the 4570 on the main board.
Pin 1:
Pin 2:
Pin 3:
Pin 4:
Pin 5:
Pin 6:
Pin 7:
Pin 8:
If so, post the AC voltage on all but pins 4 and 8 on the 4570 on the main board.
Pin 1:
Pin 2:
Pin 3:
Pin 4:
Pin 5:
Pin 6:
Pin 7:
Pin 8:
I do have 1v on pin#1 and zero on pin#7 when powered through the right RCA.
I do have 1v on Pin#7 and Zero on pin#1 when powered through the left RCA.
Is pin#1 the right output, and pin#7 is the left output on the op-amp?_
My 15amp fuse died before I could get to the c4570c on the board there has been at least two dozen powerups(10-15amp spike) on this fuse so I hope thats got something to do with it's failure. It has a small break in it, but doesn't look a fuse that blew violently. Off to work, I will post new results this evening. Thanks again for all your time and effort. Matt
I do have 1v on Pin#7 and Zero on pin#1 when powered through the left RCA.
Is pin#1 the right output, and pin#7 is the left output on the op-amp?_
My 15amp fuse died before I could get to the c4570c on the board there has been at least two dozen powerups(10-15amp spike) on this fuse so I hope thats got something to do with it's failure. It has a small break in it, but doesn't look a fuse that blew violently. Off to work, I will post new results this evening. Thanks again for all your time and effort. Matt
Amp powered up fine with the new fuse. Pins 1&7 both read equal. On this test I had 1.2v running through the RCA inputs.
For the 4570 on the half nearest the RCA's(the good side)
Pin1- 11.8v
Pin2- 2.3v
Pin3- 9.5v
Pin4- 0
Pin5- 9.5v
Pin6- 2.3v
Pin7- 11.9v
Pin8- 30.3v
The other half reads:
Pin1- .3v
Pin2- .2v
Pin3- .2v
Pin4- 0
Pin5- .2v
Pin6- .2v
Pin7- .3v
Pin8- 31.3v
For the 4570 on the half nearest the RCA's(the good side)
Pin1- 11.8v
Pin2- 2.3v
Pin3- 9.5v
Pin4- 0
Pin5- 9.5v
Pin6- 2.3v
Pin7- 11.9v
Pin8- 30.3v
The other half reads:
Pin1- .3v
Pin2- .2v
Pin3- .2v
Pin4- 0
Pin5- .2v
Pin6- .2v
Pin7- .3v
Pin8- 31.3v
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In the future, don't use a hyphen as a separator. It can be mistaken for a negative symbol when the numbers are for DC. I post the list so that you can copy and paste it into your reply.
What happened to the Fluke? It appears that you're using the red meter again.
Were you using the RCA shields as the reference (black probe)?
What happened to the Fluke? It appears that you're using the red meter again.
Were you using the RCA shields as the reference (black probe)?
Will do, no hyphens.
Fluke has dead batt. and keep shutting off on me.
Yes, RCA shields for ground.
Fluke has dead batt. and keep shutting off on me.
Yes, RCA shields for ground.
OK. There seems to be a serious problem. There should be no AC on the power supply pins of the IC.
What is the resistance from pin 4 to the RCA shields?
What is the DC voltage on pins 4 and 8 of the 4570s on the main board?
What is the resistance from pin 4 to the RCA shields?
What is the DC voltage on pins 4 and 8 of the 4570s on the main board?
Pin 4 has no resitance on either 4570 Using either ground shield (audible tone on the fluke 0.0)
DC voltage on the side near RCA's is
pin4 -13.9vdc (fluke reads neg.)
pin8 14.3vdc
The other side reads:
pin4 -13.8vdc (fluke reads neg.)
pin8 13.9
I didn't know you could have a negative DC or is an error?_
DC voltage on the side near RCA's is
pin4 -13.9vdc (fluke reads neg.)
pin8 14.3vdc
The other side reads:
pin4 -13.8vdc (fluke reads neg.)
pin8 13.9
I didn't know you could have a negative DC or is an error?_
Negative voltage is perfectly normal but it's not normal to have 0 ohms of resistance between the RCA shields and also reading negative voltage. If there was o ohms of resistance, there would be no possible way to have any significant voltage difference between the shield and pin 4.
What model fluke are you using?
What model fluke are you using?
I'll recheck and post pictures of the readings and the meter settings in a couple hrs. Unfortunatly my brother had to take the fluke back to work so I'm back to using the POS meter or the Sencore.
Rechecked and pin4 on both op-amps on the pre-amp board show zero VAC. Pin8 on both op-amps are reading 31.2vac and pictures are a bit fuzzy but should help.
The ohms section seems to be unreliable. I will have access to the fluke later tonight for ohm testing.
The ohms section seems to be unreliable. I will have access to the fluke later tonight for ohm testing.
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Set the meter to the 2000 ohm mode (not the 2000k ohm mode) and recheck. I think it's OK but having on the lower resistance setting will make it easier to understand.
Re-check the AC voltage on pin 4 and 8 with no input signal.
Re-check the AC voltage on pin 4 and 8 with no input signal.
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